Well treating fluid and process of making same



United. States. Patent 2,997,441 WELL TREATING FLUID AND PROCESS OF MAKING SAME John Wilbur Freeland, 819 W. Fern Drive,

Fullerton, Calif. No Drawing. Filed Oct. 16, 1958, Ser. No. 767,526 8 Claims. (Cl. 252-855) This invention relates to fluids for the treatment of wells, more particularly as carrying agents for particulate matter used in formation fracturing operations; and to a process of making such agents.

A technique for increasing the recovery of oil from subsurface formations penetrated by oil andgas Wells is that of so-called formation fracturing. In this process, fluid pressure is applied to the oil-bearing formation to be treated 'at a sufficiently great pressure that the formation is actually fractured outwardly from the face of the .bore hole. In some cases, and its believed generally, this fracturing takes place more or less horizontally, along the natural bedding planes of the sedimentary strata, and in other cases the fractures are believed to be vertical. In any case, the fractures so formed extend for a considerable distance from the bore hole outwardly into the oilbearing formation. It is common to include with the fluid applied in this fracturing operation a quantity of particulate matter such as sand or fine gravel, and thephysical characteristics of the fluid are so maintained that the sand or gravel is carried out into the fractures so formed. When the pressure is released, much of the fluid re-enters the well, but'the sand or gravel remains behind in the fractures as a propping agent, preventing complete closure of the fractures. This leaves a permanently permeable path for oil from the formation to reach the bore hole and thus be produced from the well. The process is par ticularly adapted to formations having low inherent permeabilities, so that in the absense of fracturing by the method described, the natural flow rate of oil into the well would be too slight. It will be seen from this brief description that the fluid used must have a number of rather special properties. In the first place, it must be able to carry the gravel or sand out along the fracture planes. In order for this to be accomplished, it is most expedient to provide some minimum suspending in the fluid. In the sec- 0nd place, it must have a known penetrating action against the face of the formation treated, particularly along the fracture faces, for otherwise the ,volume of fluid injected into the hole would have to be many times that actually used in fracturing and carrying in the gravel, and more over, ingress of foreign fluids into an oil-bearing formation is generally to be avoided. In the third place, the fracturing fluid must have the ability to be readily floated away from the face of the oil-bearing formation, especially in the fracture faces, without leaving any residual impairment of permeability. In other words, it must come away from the formation face cleanly without having plugged it in any way, when the formation is placed on production and oil begins to migrate into the fractures and eventually into the bore hole.

A number of expedients have been proposed and tried to accomplish the purposes set forth above. As may be readily imagined, however it is not easy to combine all of these properties into a single fluid, and it must be stated that the fluids now available for this purpose are not entirely satisfactory in every respect, particularly as to the three functions listed above.

An object of the present invention is to provide a fracturing fluid which has good carrying ability for propping sand and gravel. 1

Another object of the invention is to provide such a fluid which has a minimum of penetration into the sandstone or similar formations.

A still further object of the invention is to provide a fluid of the type described which has no residual impairment of any oil-bearing formation contacted, even when the fluid is compressed against the formation at fracturing pressure differentials.

A further object of the invention is to provide such a fluid which is inexpensive and convenient in the manufacture thereof.

Other objects of the invention Will appear as the description thereof proceeds.

Generally stated, and in accordance with an illustrative embodiment of the invent-ion, a calcium tallate soap is formed in the presence of finely divided calcium sulfate, and is formed through the medium of an aqueous solution or dispersion of a previously formed sodium tallate soap. The intimate mixture of calcium tallate soap and finely divided calcium sulfate resulting is dried and ground, with additional lime optionally incorporated, to form an additive which when mixed with a petroleum oil, such as kerosene, diesel fuel, crude oil or other petroleum fractions, forms a fracturing fluid having the suspending properties, that is, able to maintain said granules in suspension, and at the same time has a low fluid loss when tested against a permeable formation, and has the ability to be flushed or floated away from the face of such a permeable formation with substantially zero impairment of the permeability of the latter.

In order to make my novel fluid, I take :a suitable quantity of tall oil, which is a welLknow and well-defined product of the sulfate pulp industry, and which consists largely of about 50% fatty acids, largely o leic and other unsaturated fatty acids, about 40 or 45% rosin acids, principally abietic acid, and the balance higher alicyclic alcohols, i.e., sterols. This is added to a warm solution of caustic soda, in approximately stoichiometric proportions. For example, I may mix 12 pounds of caustic soda in 25 gallons of water then stir in 100 pounds of hot tall oil having a temperature of 200240' F. Simple stirring suflices to complete the saponification of the sodium soap and the solution is then diluted with water to a volume of 42 gallons. Then, in a separate container, I suspend 15.0 pounds of quick lime and 12.5 pounds of dead-burned gypsum into 125 gallons of water at approximately 95 F., 25.2 gallons of the aqueous dispersion of sodium tall oil soap prepared as described above isthen pumped into the lime-gypsum warm water mixture just described, agitation being continued for 25 minutes, preferably using a centrifugal pump with a bow tie shaped impeller capable of aerating the mixture during agitation. After circulation of the reactants as described, the mixture is pumped into open top drums, whereupon the calcium tallate soap-gypsum. aggregate floats to the top, this action being assisted by the aeration given during the previous agitation. The underlying water is drawn OE and the soap cakes are removed, drained over-night, crushed so as to facilitate drying, and put on drying trays and dried at approximately F. to 125 F. for two days. This results in a dry mass which can be readily ground, for example, in a hammermill. I prefer to grind the product so that to thereof passes a 100 mesh screen. During the grinding operation, I may add approximately 10 pounds of a hydrated lime per hundred pounds of the product of the drier, the latter being the calcium tallate-gypsum aggregate. The hydrated lime acts as a grinding aid, and also improves the properties of the final composition.

In preparing my new fracturing composition, as afore said, I have found it desirable to use the calcium sulfate component, which is preferably dead burned gypsum, in an amount that will result in my composition having 10 3 to 30% by weight of dead-burned gypsum based on the weight of the calcium tallate in said composition.

In order to prepare a fracturing fluid from this mixture, I add, for a typical fluid, pound of the ground product as described above to a gallon of fracturing 'oil, such as, for example, crude oil. The desired propping mixture, such as, for example, one to four pounds of sand, such as 2030 mesh Ottawa sand, may then be added to complete the fracturing fluid-propping sand miX- ture. The great efficiency of the product made in accordance with my invention may be seen from the remarkable fact that merely of a pound added to a gallon of oil suflices to impart the desired properties thereto for use as a fracturing fluid.

The steps in my newly invented process and the ingredients which enter thereinto have been carefully chosen so as to cooperate to form a novel resulting composition having a unique ability to perform the requisite functions as described above. It is essential, for example, that the calcium soap be formed in the presence of the finely divided gypsum, and formed from a previously saponified tall oil in water-dispersible form, such as the sodium soap which has been described. A large number of tests which I have made show conclusively that the superior results which I obtain result from this unique series of steps performed upon the specified ingredients. I have not been able to ascertain unequivocally and with finality the precise reasons for the remarkable behavior of my composition, but offer some theoretical explanations, to which, however, I do not wish to be bound. They are offered by way of a reasonable explanation. In the first place, the gypsum has an important function of neutralizing or cleaning up, by simple metathesis, of any residual sodium hydroxide which would otherwise possihly carry over from the first step of the process. In the second place, when the calcium soap is formed in the presence of the finely divided gypsum, which is chemically calcium sulfate, of course, I believe that the calcium-ioncontaining surface of the particles of gypsum acts as a desirable nucleus for the calcium soap to aggregate about, possibly leading to some surface orientation of calcium soap on the gypsum particles, and in any case evidently permitting great ease of re-dispersion of the dry, powdered composition when it is made into a formation treating fluid. A third function performed by the gypsum is that of a finely divided bridging agent against the pores of the formation treated, thus aiding in the attaining of a low fluid loss. A fin'ther characteristic of the gypsum particles is that by reason of their slight water solubility, they may eventually be dissolved over a long period of time as the well is produced, should any of them be left behind in the fractured formation,

Some ranges of proportions and specifications for the various components of my composition will now be given. The tall oil used is a standardized article of commerce, but will naturally vary somewhat in acid number from producer to producer, and even from season to season. The amount of caustic soda used is, as has been indicated, that required to react stoichiometrically with the tall oil, which may readily be determined by anyone skilled in the art, having ascertained the acid number of the latter. A leeway of :10% in the amount of caustic soda thus determined is practicable. The amount of quick-lime used in forming the calcium tallate soap, which, of course, may also be hydrated lime if desired, should again be chosen on a stoichiometric basis, and the amount actually used may vary from about 20% to +20% of the theoretical amount for complete reaction. The gypsum preferably should be dead-burned, as indicated, and should be ground to at least 90% passing an 80 mesh screen, and preferably somewhat finer. The lirne optionally added during. the grinding operation may vary from zero to about 25% by weight of the calcium tallate-gypsum mix. As noted, 10% is preferred. The fluid used for the formation. treatment may be any petroleum oil or .into hydrated lime since it is added to water.

fraction thereof, as has been indicated. Considerations of economy usually dictate the oil chosen, which is most frequently a crude oil although a diesel oil or fuel oil, or similar cut, can be used. The amount of my calcium soap-gypsum composition to be used will vary somewhat from oil to oil in accordance with the suspension properties needed. All ofthis, of course, is well within the skill of the art. In general, from to of a pound of my calcium tallate soap-gypsum mixture suffices for a gallon of oil. To the oil thus prepared, 1 to 4 pounds of sand or gravel may be used. The dispersing properties of my dry composition are so remarkable that simple addition of the dry composition to the oil, followed by a minimum of pumping or other agitation, suflic'es to develop the desired properties.

A number of test results will now be given, from which the great superiority of my composition over ordinary calcium tallate soap will be seen:

Example 30 min. Soap: fluid loss, cc. Pure Ca-tal-late 9.5 My Ca-tallate-gypsum 4.4 My Ca-tallate-gypsum plus 10% lime 2.3

No'rns.'lhe soap was added at 1.14% 01' the 011, w./v. 24 gms. sand were added for each cc. of oil used. The fluid loss was measured after 30 minutes test.

In accordance with the terminology used in this art, the soap formed from tall oil with an alkaline material is referred to as a tallate or sometimes simply as a tall oil soap. Lime is used to denote interchangeably quick-lime or hydrated lime, either of which may be used. Quick-lime of course is more or less instantly changed Deadburned gypsum which I prefer for the gypsum usedin accordance with my invention again is a term of the chemical art, and refers to gypsum which has been fired in a kiln or other furnace until all of the water of constitution originally present has been driven off.

It will be apparent to those skilled in the art that a. number of modifications and changes may be made in my invention, all relating to the same inventive result, and it is intended that the claims appended hereto be interpreted broadly, within the scope and spirit of the invention.

What I claim is:

1. A process of preparing a dry composition useful for producing formation treating fluids, comprising: forming an aqueous dispersion of a sodiumtallate soap; forming a second dispersion of lime and gypsum in water, mixing the two suspensions so formed in such proportions that substantially complete formation of calcium tallate soap results and so that said gypsum is present to the extent of about 10% to about 30% by weight of said calcium tallate, recovering the solids from the reacted mixture, and drying and grinding said solids to form a dry powder.

2. The process in accordance with claim 1 wherein the sodium tallate soap is made up in the proportions of about 12 pounds of caustic soda to 100 pounds of tall oil.

3. The process in accordance with claim 1 wherein about 15 pounds of quick-lime and 12.5 pounds of deadburned gypsum are used per 60 pounds of tall oil contained in said sodium tallate soap;

4. A process of preparing a dry compositionuseful for producing formation treating fluids, comprising:v forming an aqueous dispersion of a sodium tallate soap; forming a second dispersion of lime and gypsum in Water, mixing the two suspensions so formed in such proportions that substantially complete formation of calcium tallate soap results and so that said gypsum is present to the extent of about 10% to about 30% by weight of said calcium tallate, recovering the solids from the reacted mixture, drying and grinding said solids with added lime to form a dry powder.

5. A formation treating fluid comprising: a petroleum oil having dispersed therein a minor amount of a dry powdered composition resulting from the precipitation of a calcium tallate soap with about 10% to about 30% of its weight of finely divided dead-burned gypsum in aqueous suspension, said calcium tallate soap being so formed from a sodium tallate soap and lime.

6. The fluid of claim 5 in which the dry powdered mix 6 is present in the proportion of A to $5 pound per gallon References Cited in the file of this patent UNITED STATES PATENTS 2,623,015 Fischer Dec. 23, 1952 2,779,735 Brown et al Ian. 29, 1957 2,793,996 Lummus May 28, 1957 2,801,218 Menaul July 30, 1957 2,825,409 Ring Mar. 4, 1958 

1. A PROCESS OF PREPARING A DRY COMPOSITION USEFUL FOR PRODUCING FORMATION TREATING FLUIDS, COMPRISING: FORMING AN AQUEOUS DISPERSION OF A SODIUM TALLATE SOAP, FORMING A SECOND DISPERSION OF LIME AND GYPSUM IN WATER, MIXING THE TWO SUSPENSIONS SO FORMED IN SUCH PROPORTIONS THAT SUBSTANTIALLY COMPLETE FORMATION OF CALCIUM TALLATE SOAP RESULTS AND SO THAT SAID GYPSUM IS PRESENT TO THE EXTENT OF ABOUT 10% TO ABOUT 30% BY WEIGHT OF SAID CALCIUM TALLATE, RECOVERING THE SOLIDS FROM THE REACTED MIXTURE, AND DRYING AND GRINDING SAID SOLIDS TO FORM A DRY POWDER. 